This invention relates to a liquid phase epitaxial growth method, and more particularly, to an epitaxial growth method which may be used in the production of an extremely thin epitaxial growth layer.
A liquid phase epitaxial (LPE) growth method, in which a III-V group compound semiconductor such as GaAs, InP, etc., has been used as the principal method of growing epitaxial layers. The advantages of such LPE method is that crystals of high quality may be readily obtained, but the method has a drawback in that it is difficult to form extremely thin films of less than approximately 500 .ANG.. The reason is that it is so difficult to control the thickness of the epitaxial growth layers in such method is that the growth speed is inherently fast and the growth time is short. Therefore, in the growth of extremely thin epitaxial films or in the growth of multi-quantum well epitaxial layers, formed by accumulating a plurality of extremely thin epitaxial layers, a molecular beam epitaxy (MBE) method, a vapor phase epitaxy (VPE), and a metal organic chemical vapor deposition method (MOCVD) are used. However, these methods are generally inferior to a liquid phase epitaxial method in that the apparatuses used for such methods are expensive and it is difficult to obtain good crystal characteristics from such methods.
In a conventional LPE growth method for producing crystals, a growth boat is used which has a growth solution holder and a substrate holder. The growth solution holder and substrate holder are designed such that one is slidable in respect to the other. The growth of crystals is carried out by stopping the movement of the solution on the substrate and by contacting the solution and the substrate for a predetermined time. Suppose that, in this conventional method t.sub.1 represents the time for completely contacting the solution with the substrate, t.sub.2 is time for maintaining contact between the solution and the substrate and t.sub.3 is the time for completely wiping-off the substrate from the solution by re-starting the sliding operation of the substrate. The crystal is grown on the substrate in transition time (t.sub.1 +t.sub.3) when the substrate is slid in respect to the substrate, as well as in time t.sub.2 ; therefore, it is impossible to precisely define the effective growth time. In case of a long time growth, the time (t.sub.1 +t.sub.3) is negligible. However, in case of a short time growth, it is extremely difficult to control the thickness of an extremely thin growth layer with high reproducibility, since it is impossible to control the growth time.
To suppress the transition time to the extent possible, a growth method has been employed which uses a vertical-type rotary growth boat (see the Journal of Electronic Materials, Vol. 9, 1980, pp 1-27, by E. A. Rezek et al.). In this method, a member for sliding the boat is directly connected to a drive motor and, therefore, the transition time is reduced. However, there is a limit in respect to reducing the transition time by use of this method, and therefore the method cannot become the best improvement method. Further, the method uses a vertical boat, and it is complicated to insert a boat into the reactor and remove the boat therefrom as compared with methods employing a horizontal boat. Since the size of the substrate is determined by the diameter of the reactor tube, it is difficult to obtain a wide effective space and the method is therefore not suitable for mass production. Still further, in cases where such method is used for applying buried epitaxial growth layers on a substrate in which mesas or grooves are formed in a stripe-shaped manner, there occurs deviations in the thickness of extremely thin epitaxial growth layers on a substrate since sliding speed differs between the rotary center portion of the substrate and the outer edge portion thereof.